Texture for a fireplace
Sounds like the job for a Voronoi texture. While not exactly the same you can approximate that pattern relatively closely.

You can either apply it at material level, as a Bump map or as material based displacement, or you can use it as geometry level with a Displacement Node.

Last option will produce actual geometry but most likely require very high levels of subdivision and hence very dense geometry.


Shader Bump Map

Material Displacement

Geometry displacement